Parathyroid hormone and growth in children with chronic renal failure

Background. In pediatric chronic renal failure (CRF) optimal parathyroid hormone (PTH) concentrations that minimize renal osteodystrophy and maximize growth are unknown. The search for optimum concentrations has been complicated as currently used intact PTH (iPTH) assays cross-react with long carboxyl-terminal PTH fragments (C-PTH), which antagonize the biologic actions of 1-84 PTH. The purpose of this study was to investigate the relationship between PTH, the 1-84 PTH:CPTH ratio and growth rate in children with CRF. Methods. A total of 162 patients, median (range) age 9.9 years (0.3 to 17.1 years), were recruited: 136 with a glomerular filtration rate (GFR) <60 mL/min/1.73 m(2) [96 managed conservatively (CRF group) and 40 transplanted patients], and 26 dialysis patients. Over a median (range) period of 1.1 years (0.5 to 1.7, ears), children attended five (three to 15) clinics at which iPTH, cyclase-activating PTH (CAP-PTH), and height were measured. Results. Mean PTH concentrations were within the normal range for both assays for the CRF group and up to twice the upper limit of normal for the dialysis groups CAP-PTH 24.8 pg/mL and 59.9 pg/mL (normal range 5 to 39 pg/mL), iPTH 37.1 pg/mL., and 102.6 pg/mL, respectively (normal range 14 to 66 pg/mL). The patients grew normally (change in height standard deviation score per year (Delta HtSDS) = -0.01). There was no relationship between PTH concentrations and Delta HtSDS in any patient group. The 1-84 PTH:C-PTH ratio was lower in dialyzed patients (P = 0.003), with worsening renal function (P = 0.047) and with PTH concentrations outside the normal range (P = 0.01). There was a weak correlation between the 1-84 PTH:C-PTH ratio and the Delta HtSDS (r = 0.2, P = 0.01). Conclusion. Normal range PTH concentrations are appropriate, allowing normal growth in children with CRF managed conservatively. C-PTH may be of clinical significance.